Shadow only cared about looking for the formula for immortality. Being a powerful and invincible warrior who wins regardless of who his opponent is. He will protect the world from danger no matter what he needs to do to achieve his goal.

This is his main objective and focus. There is a lot he has lost and suffered in the past and he doesn't want to go through that again. He doesn't trust others and works better alone. He has no time or interest in trivial or silly things. His heart is bitter and closed. Or that's what he thought until he met you.

Somehow you managed to get past the barriers he created and melted his heart completely. Shadow tried to deny it, to close himself off, but in the end he ended up completely surrendering to you. You have become absolutely everything to him.